Manufacture of evaporated layers



April 1, 1958 H. G. LUBSZYNSKI MANUFACTURE OF EVAPORATED LAYERS Filed July 19; 1955 xxXxXXXXxXXXx v 11:20 612201 E Gila/bag United States Patent MANUFACTURE OF EVAPORATEK LAYERS Hans Gerhard Lubszynski, Lawrence, England, assign-or to Electric & Musical Industries Limited, Hayes, Mid- This invention relates to the formation of evaporated layers.

Layers of evaporated material are frequently required as, for example, in electron discharge devices. In one type of electron discharge device a target electrode is formed by evaporating a layer of photo-conductive material on to a glass window at the end of an envelope and this layer is arranged to be scanned by an electron beam. Such a device is suitable for the generation of signals for television and similar purposes, these signals being generated during scanning of the target electrode by the electron beam after the point-to-point conductivity of the target electrode has been changed by projecting an optical image thereon.

In one form of target electrode, composed of photoconductive material such as antimony trisulphide, zinc selenide or cadmium sulphide, it is desirable that the layer should be deposited so that it is of a spongy nature. For the formation of such a spongy layer it has been proposed see Patent No. 2,744,837 to evaporate antimony trisulphide in the presence of air at a fairly high gas pressure such as 1 millimetre or more of mercury. It is found that when evaporating in air it is necessary to employ the fairly high gas pressure above referred to in order to slow down the molecules of the evaporated material to an extent to cause the deposition of a spongy layer. Slowing down of the evaporated material is caused by collisions between the molecules of the material and the gas atoms and the higher the gas pressure the more collisions occur in slowing down the molecules in order to cause themto stick together to form large particles necessary for the formation of a spongy layer. The larger, however, the number of collisions the greater is the scattering of molecules so that a smaller fraction of the evaporated material is deposited on the required area.

The object of the present invention is to provide an' improved method of depositing a spongy layer of evapxenon. Xenon has a molecular weight of about 130 which is considerably higher than that of air, hence the energy transfer per collision is greater, and as a result lower gas pressures may in some cases be employed resulting in less scattering of the evaporated material.

In order that the said invention may be clearly understood and readily carried into efiect, it will now be more fully described with reference to the accompanying drawing, which illustrates a portion of an electron discharge device employing an evaporated layer in accordance with the invention.

As shown in the drawing, reference numeral 1 indicates the envelope of the discharge device having a glass end wall 2 provided with a transparent signal electrode 3 on to which a spongy layer 4 is required to be formed. The device shown in the drawing is provided with a cylindrical electrode 5 the end of which adjacent to the window 2 is provided with a mesh 6. The envelope l is provided with a side tube 7 by means of which, in known manner, a source S of material to be evaporated to form the layer 4 can be introduced so as to be disposed substantially centrally with respect to the window 2. This source 8 can be manipulated magnetically into and out of the envelope in known manner when required. The source 8 may comprise a boat containing antimony trisulphide or some other suitable photo-conductive material. In order to form the spongy layer 4 the envelope 1 is first evacuated and then Xenon is introduced into the envelope and with the source 8 in the position shown in the drawing heating current is applied to the source in order to cause evaporation of the antimony trisulphide. The preferred gas pressure is 0.36 millimetre of mercury. The gas pressure should not, however, be less than 0.3 millimetre of mercury although higher pressures may be employed, for example 0.7 millimetre of mercury. If during the evaporation process the mesh 6 becomes clogged with the evaporated material, then the mesh can be cleared of said material by heating the mesh by eddy current heating. Since a lower gas pressure may be used compared with the case when air is employed, the mesh does not require to be heated to such a high degree as 450 C. when air is employed, so that there is less danger of wrinkling the mesh and also of causing decomposition of the evaporated material.

After the evaporation process has been completed and a desired thickness of spongy layer has been formed, the envelope is evacuated, the boat 8 removed and the side "tube 7 is then sealed off from the envelope 1.

What I claim is:

1. The method of depositing a spongy coating of photoconductive material on a surface in the interior of an envelope which comprises inserting the photo-conductive material in the envelope, evacuating the envelope, introducing xenon into the envelope at a pressure of 0.3 to 0.7 mm. of mercury and heating the photo-conductive material in the presence of Xenon to evaporate it to cause deposition of a spongy coating of photo-conductive material on said surface.

2. The method according to claim 1, in which said photo-conductive material is selected from the group consisting of antimony trisulphide, zinc selenide and cadmium sulphide;

ReferencesCited in the file of this patent UNITED STATES PATENTS 2,642,367 Pfund June 16, 1953 2,654,852 Goodrich Oct. 6, 1953 2,744,837 Forgue May 8, 1956 Forgue et a1. May 8, 1956 

1. THE METHOD OF DEPOSITING A SPONGY COATING OF PHOTOCONDUCTIVE MATERIAL ON A SURFACE IN THE INTERIOR OF AN ENVELOPE WHICH COMPRISES INSERTING THE PHOTO-CONDUCTIVE MATERIAL IN THE ENVELOPE, EVACUATING THE ENVELOPE, INTRODUCING XENON INTO THE ENVELOPE AT A PRESSURE OF 0.3 TO 0.7 MM. OF MERCURY AND HEATING THE PHOTO-CONDUCTIVE MATERIAL IN THE PRESENCE OF XENON TO EVAPORATE IT TO CAUSE DEPOSITION OF A SPONGY COATING OF PHOTO-CONDUCTIVE MATERIAL ON SAID SURFACE. 